(1) Field of the Invention
This invention relates to aluminum base bearing alloys and bearing materials and, particularly, to aluminum base bearing alloys in which a specified number of coarse intermetallic precipitates of a specified size are dispersed in the aluminum matrix.
(2) Background of the Invention
Aluminum alloys are widely used as bearings in internal combustion engines, e.g., as connecting rod bearings and crankshaft bearings in automobile and marine engines. These bearings are resistant to corrosion in the engine environment and thus are highly advantageous for such use.
Materials employed as bearings in internal combustion engines are required to withstand high loads and high temperatures. Much effort has been directed in recent years, therefore, to providing aluminum base bearing alloys having high resistance to seizure, fatigue and wear under the conditions encountered in these engines.
U.S. Pat. No. 4,153,756 discloses Al-Sn base bearing alloys having a low degree of softening and, consequently, high fatigue strength, under high temperature conditions. The alloy is provided by adding chromium or zirconium to a basic alloy consisting of 10 to 30 wt.% tin and the remainder aluminum. Copper or both copper and beryllium can also be added to the alloy.
Al-Sn base bearing alloys comprising 3.5-35 wt.% of Sn, 0.1-1.0 wt.% of Cr and 1-10 wt.% in total of one or more members selected from Si, Cr, Mn, Sb, Ti, Zr, Ni and Fe, the remainder being aluminum, are also disclosed in the prior art as having high fatigue strength and, additionally, good wear resistance.
G. C. Pratt and C. A. Perkins in a paper entitled "Aluminum Based Crankshaft Bearings for the High Speed Diesel Engine", SAE Technical Paper Series 810199 (1981), describe the development of an engine bearing lining alloy for the high speed diesel engine and which has the composition Si (11 wt.%), Cu (1 wt.%) and the remainder of Al. The alloy is described as having superior seisure resistance as compared to lead bronze on test rigs under conditions of sparse lubrication and controlled misalignment. It is further described that the casting procedure adopted and the subsequent processing of the alloy to bimetal ensure that the silicon particles are restricted to a few microns in size and that the silicon particle size in an important factor in determining the extent of compatibility (defined in the paper as the resistance of a bearing alloy to local welding on to a steel counterface); the highest degree being obtained only when there is a complete absence of coarse particles. The casting procedure and processing of the alloy to bimetal, however, are not described.
The mere inclusion of silicon or of other elements which form precipitates in an aluminum base bearing alloy, however, does not ensure that the bearing alloy will possess consistently superior resistance to seizure, fatigue and wear under the severe loads and temperature conditions encountered in modern internal combustion engines and, particularly, in automobile engines which have shafts made of spheroidal, or nodular, graphite cast iron or other coarse material.
It is an object of the present invention, therefore, to provide an aluminum base bearing alloy and bearing composite which consistently possesses a superior balance of seizure, fatigue and wear resistance under high loads and high temperatures and when used as a bearing surface with nodular cast iron materials.